In article , roddy
writes
This is the first year I have grown courgettes.
Have followed a rigorous watering regime and weekly liquid feed; but the
fruit is suffering from blossom end rot and develop into small marrows very
quickly.
Am I over watering and feeding?
Quite possibly. Take off all rot affected fruits. Stop feeding them and
water them only once per day for a while until you see an improvement.

Rapid development into marrows can be encouraged by (over) generous
feeding and watering, but it is more likely to be an outcome of the
plant type. We grow marrows from the Green Bush or All Green Bush
variety, and their fruits can be taken as courgettes when they are very
small, but for specifically courgette production, we prefer the
Zucchini types such as Nero de Milan, Defender F1 etc. They are deeper
green, better shaped and better flavoured at courgette size. If left on
the plant, they would eventually develop into marrows, but that will
inhibit more courgettes from developing on the plant.
--
Alan & Joan Gould - North Lincs.